species, and, in some cases, each individual, has its
own particular autumn and spring. There is no hibernation nor aestivation
(except by land shells); birds have not one uniform time for
nidification; and moulting extends from February to May.

Amazonia, though equatorially situated, has a temperate climate. It is
cooler than Guinea or Guiana. This is owing to the constant evaporation
from so much submerged land, and the ceaseless trade winds. The mean
annual temperature of the air is about 81 deg..[166] The nights are always
cool. There are no sudden changes, and no fiery "dog days." Venereal and
cutaneous affections are found among the people; but they spring from an
irregular life. A traveler on the slow black tributaries may take the
tertiana, but only after weeks of exposure. Yellow fever and cholera
seldom ascend the river above Para; and on the Middle Amazon there are
neither endemics nor epidemics, though the trades are feebly felt
there, and the air is stagnant and sultry. According to Bates, swampy
and weedy places on the Amazon are generally more healthy than dry ones.
Whatever exceptions be taken to the branches, the main river is
certainly as healthy as the Mississippi: the rapid current of the water
and the continual movement of the air maintaining its salubrity. The few
English residents (Messrs. Hislop, Jeffreys, and Hauxwell), who have
lived here thirty or forty years, are as fresh and florid as if they had
never left their native country. The native women preserve their beauty
until late in life. Great is the contrast between the gloomy winters and
dusty summers, the chilly springs and frosty autumns of the temperate
zone, and the perennial beauty of the equator! No traveler on the Amazon
would exchange what Wallace calls "the magic half-hour after sunset" for
the long gray twilight of the north. "The man accustomed to this climate
(wrote Herndon) is ever unwilling to give it up for a more bracing one."

[Footnote 166: Agassiz calls the average temperature 84 deg., which, it
seems to us, is too high. The mean between the temperatures of Para,
Manaos, and Tabatinga is 80.7 deg..]

The mineral kingdom is represented only by sand, clay, and loam. The
solid rock (except the sandstone already mentioned) begins above the
falls on the tributaries. The precious gems and metals are confined to
the still higher lands of Goyaz, Matto Grosso, and the slopes of the
Andes. The soil on the Lower Amazon is sandy; o